Cesca, 2011. Source inversion in mining environments AIM 2 nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Seismic source inversion in mining environments Simone Cesca Institute of Geophysics, University of Hamburg [email protected]http://mine.zmaw.de
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Seismic source inversion in mining environments Simone Cesca
Seismic source inversion in mining environments Simone Cesca Institute of Geophysics, University of Hamburg [email protected] http://mine.zmaw.de. Outline The MINE project background, structure and project aims Seismic source inversion problem theory and methods - PowerPoint PPT Presentation
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Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Source inversion in seismology using the Kiwi tools
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Point source model, double couple & moment tensor
More complete point source model is represented by a moment tensor (MT)
MT = MTDC + MTCLVD + MTISO
Earthquakes is often well modeled in terms of shear cracks, using a point source representation (DC model).
after Hasegawa et al. (1989)
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Extended source model, definitions
Extended sources may be reproduced by superposition of several point sources distributed along a planar (or bended) rupture surface. Each point source start radiating when reached by the rupture front. Radiation lasts for a given (rise) time.
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
The eikonal source model
Circular area, plus constraints
Rupture velocity scales with shear velocity
Despite its flexibility, the eikonal source model is described by only 13 parameters (considering constraints and earth model as fixed and known)
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
One earthquake, five solutions
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Source model parameters and inversion priorities
Source model parameters (13)
Time Lat Lon Depth M0 Strike Dip Rake NucX NucY RuptV RiseTRad
General source description
Source location Radiation pattern Rupture process
Scale of source model
Point source Finite source
Information from data
Low frequencies High frequencies
Inversion priority
Step 1, 2 Step 3
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Greece,
Shallow earthquakes
2003-2007
extended sources
Cesca et al. JGR 2010
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Source inversion, natural and induced seismicity
Cesca et al. submitted
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Source inversion in mining environment
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Bischoff et al. 2010
Ruhr region
Coal mining induced seismicity monitored by Ruhr University since 1983
About 1000 events are recorded between 0.7<ML<3.3 every year
Hamm region (blue circle)
>7000 events in 2006-2007 (14 months)
913 events 0.0<ML<2.0
DC inversion
MT inversion
Kinematic inversion and rupture modeling
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Seismicity follows longwall mining,
Epicenters are spreaded over an area of about 2x2km
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
DC inversion results overview
Successful inversion for 578 (over 913)
Magnitude range, Mw 0.3-1.8
Very similar mechanisms
Normal faults (80%) or oblique-normal
One steep plane, one sub-horizontal
Different strike are observed, strike angles are related to mining geometry
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Wehling-Benatelli (2011)
Courtesy D. Becker
Waveform similarity analysis and
cluster analysis (relocated events)
Consistent focal mechanisms for
Major clusters
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Moment tensor / extended source parameters
Full MT solutions significant for more than 100 events
Non-DC terms results are still ambiguous
Possible inversion artefact rather than source features
Preliminar kinematic inversion for 24 largest events (Ml > 1.0)
Kinematic model is significant for 8 events, only
In almost all cases (7), the vertical rupture plane is preferred
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Conclusions
Full waveform moment tensor inversion successfully applied to mining induced seismicity at local scale (<2km) for low magnitude events (at now, down to Mw 0.3).
DC and MT focal mechanisms were successfully obtained for 587 selected events
Results are in good agreement with reference, when available (about 100 events), based on first polarities and S wave polarization.
Better results are obtained for a layered model and frequency range 0.5-2Hz
Focal mechanisms are characterized by similar ruptures. Normal faulting with one steep fault plane. In general, striking angles are linked to the mining geometry.
Non-DC resolution to be judged
Preliminar kinematic modeling for largest events (Ml≥1.0) point to a similar rupture mechanism along sub-vertical planes.
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha
Thanks to:
A. T. Şen, Prof. Dr. T. Dahm, Dr. S. Heimann, F. Grigoli, S. Maghsoudi, A. Rohr,
M. Bischoff, T. Meier, S. Wehling-Benatelli
BMBF project MINE
GEOTECHNOLGIEN programme
The Kiwi tools are currently used at:
University of Hamburg, University of Potsdam, BGR Hannover, GFZ Potsdam,
University of Coimbra, Aristotle University of Thessaloniki ,Ruhr University Bochum
Further info on software and applications:
http://mine.zmaw.de
http://kinherd.org
Cesca et al., JGR 2010
Cesca et al., J. Seismol. 2010
Cesca et al., J. Seismol., submitted
Cesca, 2011. Source inversion in mining environments
AIM 2nd annual meeting, 29-30.9.2011, Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha